AC2261 Certificate of design work

Document type: Practice Note
Title: Certificate of Design Work (CoW)
Document number: AC2261
Version: 1
1.
Purpose
The purpose of this practice note is to provide some clarity around the content and requirements of
the Certificate of Design Work (CoW), which is provided in respect to Restricted Building Work
(RBW).
2.
Legislative requirements
Section 45 of the Building Act 2004 states that if an application for a building consent is
accompanied by plans and specifications that contain design work (relating to building work) that is
RBW, then that design work must be carried out or supervised by one or more licensed building
practitioners who are licensed to carry out or supervise that work.
Further, that the plans and specifications that contain the design work must be accompanied by a
certificate of work:a)
provided by one or more licensed building practitioners who carried out or supervised that
design work; and
b)
that identifies that design work; and
c)
that states:i. that the design work complies with the Building Code; or
ii. whether waivers or modifications of the Building Code are required and, if so, what
those waivers or modifications are
RBW does not include building work for which a building consent is not required.
3.
Restricted Building Work (RBW) - Design
An application for building consent must include a CoW if the design involves RBW. The design
includes the preparation of any drawing, specification or other documentation required to
demonstrate compliance with the Building Code.
Only a licensed building practitioner (LBP) is able to design or supervise the design of RBW and
issue a CoW. If the designer does not provide a CoW the application cannot be accepted.
The Regulations require that the following design elements be designed or supervised by an LBP:• the primary structure,
• external moisture management system, or
• the fire-safety system
For a full list of definitions refer to the Building (Definition of Restricted Building Work) Order 2011
Primary structure means
a) building elements that are intended to contribute to its ability to withstand vertical or
horizontal loads (for example, its beams, bracing, columns, foundations, roof, subfloor
framing, and walls); and
b) includes any part of its primary structure
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The primary structure includes all structural elements that transfer imposed loads within the
building from the roof down to natural ground. Structural elements include rafters, ridge beams,
trusses, roof and wall bracing, wall framing and lintels, foundations, slabs, etc.
Although trusses are manufactured off-site they must still be incorporated and referenced in the
CoW. The designer is responsible for checking to ensure that the wind loading is correct and that
all point loads have been appropriately transferred.
A simple comment on the CoW will suffice, such as, trusses manufactured by (name of truss
maker) as per PS1 attached.
External moisture-management system means
(a) A system (whether comprising only one or 2 or more building elements) that is intended to
provide
i. Resistance to the penetration of the building by moisture from outside it; or
ii. Resistance to the accumulation within the building’s fabric of moisture that has
penetrated it from outside the building; and
(b)
Includes any of the building’s building elements that are, or form part of the damp-proofing,
roof-cladding or a roof cladding system, a ventilation system, wall-cladding or a wallcladding system, or water-proofing; and
(c)
Includes any part of its external moisture-management system
The external moisture-management system includes all elements of the external envelope that
deflect moisture away from, or provide an impenetrable barrier into, the building. For example:
cladding material, flashings, joinery and any secondary measures such as the drainage cavities
and any means for venting these cavities.
Note: internal membranes such as those used in wet areas (e.g. showers and bathrooms) are not
RBW; however, Council may require a producer statement for the installation of these products.
Fire-safety system, in relation to a building, means those of its building elements that are
intended to protect people, household units adjacent to it, or other property, from fire or the effects
of fire; and includes building elements that are, or are parts of,
a)
emergency warning systems; and
b)
systems intended to enable or facilitate the evacuation of the building in an emergency;
and
c)
systems intended to enable or facilitate fire-service operation; and
d)
systems intended to suppress or control fire or smoke
The design of fire safety systems does not include manufacturer or referenced design (e.g. the
design of a proprietary alarm system); however, these proprietary systems should be referenced,
in the CoW.
The design of fire walls that separate residential units is RBW, and as such, must be identified as
part of the design work on the CoW.
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4.
Definitions of house and small to medium apartment buildings
The following definitions are taken from the Building (Definition of Restricted Building Work) Order
2011. These definitions must only by used for the purposes of this Order. (Definitions from
documents such as the Acceptable Solutions or other Building Regulations must not be used or
confused with the definitions in this document and are purely for the purposes of determining
whether certain work is RBW).
House means a free-standing, fully detached building consisting of a single residential unit (or a
single residential unit and 1 or more residential facilities)
Residential unit means a building, or part of a building, that is so designed that it is more suitable
for being lived in by a single household or family than for any other use. Attached buildings such as
conservatories and decks are not considered RBW.
A minor household unit falls with the definition of a residential unit and is therefore RBW. A sleepout is not considered a residential unit.
Residential facility means a part of a building that is not a residential unit, but is a facility (for
example a corridor, foyer, garage, laundry, lift, sauna, or storage unit) whose principal or only
purpose is ancillary to the use of a residential unit in the building (or shared between 2 or more
residential units in the building). Residential facilities must be those facilities used directly in
relation to the residential unit(s).
Outbuildings such as garages, carports, bridges, swimming pools, sleep-outs, etc. are excluded
from the RBW.
Small-to-medium apartment building means a building that contains 2 or more residential units
or residential facilities (but excludes apartment buildings over 10m in height and those that include
non-residential uses such as retail space).
Small to medium apartment buildings include duplexes and terraced houses i.e. two or more
houses separated by a fire wall and includes apartment buildings or townhouses, tenanted by way
of a right to occupy, such as those within retirement villages. Shared facilities and spaces in
apartment buildings are also RBW.
Maximum calculated height, in relation to a building, means the vertical distance between the
highest point of its roof (excluding structures such as aerials, chimneys, flagpoles, and vents) and
the lowest point of the ground.
5.
Certificate of Design Work (CoW)
The memorandum (CoW) is a regulated form (Form 2A) and must contain all information
prescribed on it. The designer can print this form onto their own letterhead or attach a logo,
however they cannot alter the content.
All parts of the design of RBW must be included in the CoW.
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Council will only accept a building consent application if the CoW has been completed in a manner
that confirms all aspects of the RBW is covered. A CoW comprises of a number of pages and
therefore, must be able to be identified as a single document.
There will be times when more than one designer has done Design RBW. In these cases, all the
designers involved need to make sure their information aligns with any others involved in the
application. This is so that when the Memorandum (Certificate of Design Work) is read together it
is clear to the council that all the Design RBW has been done or supervised by LBPs licensed in
the Design class.
Two LBPs work on different aspects of the plans and specifications that are RBW (e.g. one
designs the foundations and slab and the other designs the balance of the superstructure), then
each LBP would be expected to provide a CoW for their respective parts.
A designer may choose to cover all RBW including the work performed by another LBP. In this
case the designer must provide a CoW covering all elements of design. This is similar to the
scenario mentioned in the definition of primary structure regarding trusses.
An engineer will often design foundations based on an investigation by a geotechnical engineer. In
this case, a CoW is not required from the geotechnical engineer as sub-surface investigation is not
RBW. In the event that the soil needs to be strengthened, such as might be the case where soils
are affected by liquefaction or other types of instability, then such strengthening is part of the RBW
and must be included in the CoW.
It is the lead or sole designer’s responsibility to ensure that all aspects have been incorporated into
the overall design. The lead or sole designers must provide all supplementary design and
proprietary product information as part of the building consent application and note on the CoW,
that they have relied, on the specialist design of others.
Building consent applications supported by a CoW form an LBP whose status cannot be verified,
will not be accepted.
6.
Licensed building practitioners and design classes
The design class for LBPs includes persons that have successfully applied under the Building
(Designation of Building Work Licensing Classes) Order 2010 to be licensed. Chartered
professional engineers (registered under the Chartered Professional Engineers of New Zealand
Act 2002) and Registered Architects (registered under the Registered Architects Act 2005) are
automatically deemed to be LBPs.
The designer providing the Memorandum (Certificate of Design Work) must work within their
individual competency (i.e. their personal professional expertise).
Design LBPs must hold a license for one of the three practice areas (Design 1, 2 or 3); this
depends on the category of building (for licensing purposes) that they were assessed against. It is
important to note, however, that a design LBP is not limited to only designing categories of building
that they were originally assessed for. A design LBP may submit a design on any category of
building if they believe it is within their individual competency.
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7.
References
Building (Designation of Building Work Licence Classes) Order 2010
Building (Definition of Restricted Building Work) Order 2011
Building (Forms Amendment) Regulations 2011
For further information about LBP or RBW refer to Ministry of Business, Innovation and
Employments website
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